1. Technical Field
The present invention relates to the field of positive-displacement piston pumps, and more particularly to a method for controlling the flow rate of such a pump.
An advantageous application relates to the supply of rubber to an extruder intended to form a profiled element for manufacturing a vehicle tire.
2. Related Art
Conventionally, a positive-displacement pump or volumetric pump comprises a product metering piston mounted in a cylinder of the pump body forming the metering chamber so as to slide between top dead center and bottom dead center, and means for actuating the piston, for example a cam in contact with one end of the latter.
One type of positive-displacement pump comprises a cylinder mounted so as to slide with respect to a sleeve of the pump body in order to place the metering chamber alternately into communication with an intake chamber and an exhaust chamber of the sleeve, by way of two orifices that are provided in the thickness of said sleeve and are each specific to the intake or exhaust of the product. The cylinder of the pump comprises inlet and outlet flaps that can close off the intake and exhaust orifices, respectively. For more details relating to a pump of this type, reference may be made for example to the patent application FR-A1-2 668 206.
Another type of positive-displacement pump comprises a dispensing plug mounted so as to rotate inside the sleeve of the pump body in order to place the metering chamber alternately into communication with the intake chamber and the exhaust chamber, by way of a single orifice provided in the thickness of the sleeve.
To this end, first and second groups of grooves are formed on the outer surface of the plug and are arranged so as to pass in front of the orifice in the sleeve during the rotation of the plug so as to place the metering chamber successively into communication with the intake chamber and then with the exhaust chamber.
Thus, the pumped product flows from the intake chamber to the metering chamber, and then from this metering chamber to the exhaust chamber, passing through the same orifice. For more details relating to a pump of this type, reference may be made for example to the patent application EP-A1-0 604 888.
With such continuously metering positive-displacement pumps, the piston is moved from top dead center to bottom dead center only under the effect of the pressure of the product flowing towards the metering chamber. Therefore, a lack of product pressure in the intake chamber can result in the metering chamber not being filled. The flow rate of the pump can thus be irregular.
In order to control the regularity of the flow rate of the pump, the patent application FR-A1-2 911 374 describes a method in which an electrical contact between the actuating cam of the metering piston and said piston has to be detected within a predetermined time limit starting from a reference position of the cam.
If the pressure of the product is too low during the intake phase, the piston does not reach bottom dead center and the electrical contact is detected outside the predetermined time limit. By contrast, if the pressure of the product is sufficiently high during this intake phase, the piston reaches bottom dead center and the electrical contact is detected within the predetermined time limit. In this case, the exhaust flow rate of the pump is considered to be regular.
However, for high speeds of the piston and of the dispensing means, the electrical contact between the cam and the piston can be obtained outside this predetermined time limit, for example given the inertia of the piston and the viscoelasticity of the product to be metered, even though the metering chamber is correctly filled. Moreover, such a control method is not applicable when the product to be metered is electrically conductive.